Might be possible but u got a difficult road ahead. Not sure if you have to be physically present in US for application, but To apply for OPT extension u need a job offer letter. F1 visa is non immigrant visa but if you are gonna apply for opt extension from nepal after getting job offer from your last employer or any other new employer, it might be difficult to prove that you intend to return back to US temporarirly since your new purpose is now work and not the study. Any way try for the best. You need to contact your international student center to mail you new signed i-20.